The present invention relates to a carbon fiber superior in processability and in physical properties as a composite.
The carbon fiber is in wide use not only as aeronautic and cosmic structural materials such as those for aircrafts and rockets, but also as sporting members such as tennis rackets, golf shafts and fishing rods. In addition, it is about to be used as a structural material of transportation machinery such as automobiles and ships.
In a composite using carbon fiber as a reinforcing fiber, it is necessary that superior dynamic properties such as high specific strength and specific modulus of the carbon fiber be reflected as much as possible in the physical properties of the composite. At present, however, this requirement is not always met to a satisfactory extent.
On the other hand, it is said that the poor handling characteristic and processability ascribable to the intrinsic properties of being rigid and fragile of the carbon fiber makes it difficult to obtain composites having uniform quality and performance.
In general, various sizing agents are added to carbon fiber for improving the physical properties of a composite and for stabilizing the quality and performance thereof. But there scarcely is available a sizing agent superior in compatibility with and adhesion to the matrix which constitutes the composite, and capable of improving the physical properties of the composite and also improving the bundling and handling properties and rubbing resistance in forming of the carbon fiber such as preparing and weaving. Despite of many proposals, a satisfactory sizing agent has not been found out yet. For example, a sizing agent for carbon fiber (see Japanese Patent Publication No. 15229/1982) consisting mainly of an epoxy or polyester resin in an organic solvent, which sizing agent has been said to be uniform in adhesion to carbon fiber and superior in solution stability thereof and also superior in compatibility with and adhesion to matrix, including particularly various matrix resins, is not desirable from the standpoint of working efficiency, particularly from the standpoint of environmental hygiene as well as fire and other accidents prevention.